The current tendency in high-speed electronic systems is to transfer data between integration circuits included therein at high speed. Data signals transmitted between the integration circuits may be set to have small amplitudes in order to improve the data speed. Further, an output impedance of a data transmission circuit for transmitting the data signals should be matched with an impedance of a transmission line through which the data signals are transmitted so that the data signals having a small amplitude are not deformed or distorted. When the output impedance of the data transmission circuit is not matched with the impedance of the transmission line, the data signals may have abnormal waveforms due to overshoot or undershoot. In such a case, the data signals may not be transmitted at a high speed.
On-die termination (ODT) is the technology where the termination resistor for impedance matching in the transmission lines is located inside a semiconductor device instead of on a printed circuit board. An ODT circuit may include a switching circuit to reduce power consumption. However, the impedance of the ODT circuits may vary according to process/voltage/temperature (PVT) conditions. Hence, a test for calibrating the impedance of the ODT circuits may be required prior to use of the ODT circuits.
The impedance calibration test may be executed using a ZQ calibration circuit. The data transmission circuit may generate a code signal for calibrating a pull-up drive or a pull-down drive using a ZQ resistor connected to an external device and may calibrate the impedance of the ODT circuit using the code signal, thereby executing the impedance calibration test.